Treatment of clay

ABSTRACT

A MINERAL HAVING A LAYER LATTICE CRYSTAL STRUCTURE, FOR EXAMPLE A CLAY MINERAL, IS BLEACHED BY FIRST FORMING AN INTERCALATION COMPLEX WITH, FOR EXAMPLE, UREA AND THEREAFTER BLEACHING THE INTERCALATION COMPLEX WITH AN OXIDISING BLEACHING AGENT.

United States Patent 3,567,474 TREATMENT OF CLAY Peter James Malden, Cornwall, England, assignor to English Clays Loveriug Pochin & Company Limited, St. Austell, Cornwall, England No Drawing. Filed Aug. 6, 1968, Ser. No. 750,474 Claims priority, application Great Britain, Aug. 11, 1967, 37,122/ 67 Int. Cl. C08h 17/06; C090 1/42 U.S. Cl. 106-72 Claims ABSTRACT OF THE DISCLOSURE A mineral having a layer lattice crystal structure, for example a clay mineral, is bleached by first forming an intercalation complex with, for example, urea and thereafter bleaching the intercalation complex with an oxidising bleaching agent.

BACKGROUND OF THE INVENTION This invention relates to the bleaching of minerals having a layer lattice crystal structure and, more particularly but not exclusively, is concerned with the bleaching of silicate minerals having this type of structure, for example kaolinitic clays.

It is common practice to bleach clays by a reducing process, for example by treatment with a dithionite. It has also been proposed to treat clays which contain varying quantities of organic discolouring matter with an oxidising bleaching agent, e.g. hydrogen peroxide, to bleach the discolouring matter, and with kaolinite and other fine clays which are not highly coloured this may result in an increase in the brightness, or reflectance to light, of the clay. However, in general the results obtained using an oxidising bleaching agent are not very satisfactory. It is also known that with minerals having a layer lattice crystal structure, such as kaolinite, it is possible to intercalate them with a compound, such as hydrazine, urea and certain salts of simple organic acids, so that the compound expands the layer lattice crystal structure and then occupies the spacing between the elementary mineral sheets.

SUMMARY OF THE INVENTION It has now been discovered, surprisingly, that by first intercalating a mineral having a layer lattice crystal structure, for example a clay, and thereafter carrying out an oxidising bleaching process, an increase in the brightness of the mineral can be obtained which is greater than can be obtained by an oxidising bleaching process alone.

Thus, in accordance with the present invention there is provided a method of bleaching a mineral having a layer lattice crystal structure, which method comprises treating the mineral with a complexing agent capable of forming an intercalation complex with the mineral, and thereafter bleaching the intercalation complex with an oxidising bleaching agent. I

The complexing agent used to form the intercalation complex can be, for example, urea, benzidine, octylamine, formamide, acetamide, ammonium acetate, caesium and rubidium salts of acetic, propionic and cyanoacetic acids, and the alkali metal salts of amino acids.

The oxidising bleaching agent can be, for example, hydrogen peroxide, an organic peroxy compound, e.g. peracetic acid or perbenzoic acid, chlorine, chlorine water, chlorine dioxide, potassium permanganate, an alkali metal dichromate, an alkali metal chlorate, an alkali metal chlorite, permonosulphuric o-r perdisulphuric acid or an alkali metal or ammonium salt thereof, or a compound capable of forming hydrogen peroxide on contact with water.

Patented Mar. 2, 1971 Advantageously after completion of the oxidising bleaching process the intercalation complex is decomposed by heating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In one procedure for carrying out the method of the invention, the mineral having a layer lattice crystal structure, for example kaolinite, is caused to form an intercalation complex by, for example, the method described by A. Weiss, W. Thielepape, G. Goring, W. Ritter, H. Schafter in Proceedings of the International Clay Conference Stockholm 1963 at pages 287 and 305. The intercalation complex is then stirred into an aqueous solution of the bleaching agent and the mixture allowed to stand for a period of time which will depend on the temperature, on the nature and concentration of the bleaching agent, and on the degree of bleaching required.

In one embodiment of the invention, the bleaching agent is hydrogen peroxide, and the mixture of intercalation complex and bleaching agent is allowed to stand at an acid pH, preferably not greater than 4.5, for from 2 to 5 weeks at room temperature. At the end of this period the mixture is then boiled for at least six hours and the bleached mineral recovered in a conventional manner.

The invention is illustrated by the following examples.

Example 1 50 grams of a fine grade paper-coating clay having reflectances of 88.0 and 92.3% at 458 and 574 m respectively, were converted, in 88% yield, to a urea intercalation complex by soaking the clay in a strong urea solution for three months. The intercalation complex was then stirred into 200 mls. of 100 volume hydrogen peroxide at pH 4.5 and allowed to stand for five weeks. The suspension was then boiled for eight hours, the pH adjusted to 4.5 and filtered. The clay was then boiled in water for a further 24 hours to decompose any residual urea intercalation complex. The recovered clay had reflectances of 93.2 and 95.3% at 458 and 574 m respectively.

When another quantity of the same clay was treated with the hydrogen peroxide, without prior formation of the urea intercalation complex, there was obtained a prodnot having refiectances of 91.4 and 94.4% at 458 and 574 m respectively.

Example 2 200 gm. of a fine grade paper-coating clay comprising by weight of particles smaller than 2 microns equivalent spherical diameter was slurried with 550 gm. of urea and 500- ml. of water and the mixture was left at a temperature of 20 C. for 10' weeks. At the end of this time the mixture was filtered and the filter cake was reslurried without washing with a further 850 gm. of urea and 500 ml. of water. The resultant slurry was left to stand at 40 C. for 10 weeks, at the end of which time the slurry was filtered. Investigation by X-ray diifraction showed that between 70 and 90% of the kaolinite was converted to the urea-kaolinite intercalation complex. The urea-kaolinite intercalation complex was then divided into six portions which were subjected to the following treatments:

Treatment 5Treated with a bleaching agent in the form of a 5% ammonium perdisulphate.

6-=-Treated with a bleaching agent in the form of a 40% peracetic acid.

TABLE I Percent reflectance to 7 t o Portion N0.: 7;

As a comparison six further portions 7 to 12 of the same clay, which had not beensubjected to treatment with urea to form a urea-kaolini t e intercalation complex, were treated in the same way asportions '1 to 6.

Portion No.

'7No treatment; '8Boiled with water for 2 hours.

Treatment 9 "9Treated at pH 4.5 with a bleaching agent in the form of a'100 vol. {30%) H 0 solution then boiled for 4 hours. 7 'lO-Treated with a bleaching agent in the form of a 6.3% chlorine solution. ii 1 11Treated with a bleaching agent in the form of 5% ammonium prdisulphate. 12Treated with a bleaching agent in the form of a 40% peracetic acid.

The treatment of portions 9 to ;l2 with the oxidising bleaching agents was performed iniexactly the same way as the treatment of portions 3 to 6. At the end of the treatment each portion was filtered, the filter cake was redispersed in water and the pH adjusted to 4.5 before refiltering and drying. V i

The reflectance of each portion to light of wavelengths 458 and 574 millimicrons, respectively, was measured 'with an Elrepho brightness meter and the results are given in Table II below.

7' TABLE II :It can be seen that in each case a greater improvement in brightness on treatment with an oxiding bleaching agent was obtained if the clay was first treated with urea to form the urea kaolinite intercalation complex.

I claim: 1 ,7

1. A method of bleaching a clay mineral having a layer lattice crystal structure, which method comprises contacting the claymineral in aqueous suspension with a complexing agent capable of forming an intercalation complex with the clay mineral, so as to form an intercalation complex therewith, and thereafter bleaching the intercalation complex with an oxidising bleaching agent.

2. method according to claim 1, wherein the intercalation complex is decomposed by heating after completion of the'oxidising bleaching process. 7

3. A method according to claim 1, wherein said clay mineral having a layer lattice crystal structure is a kao linitic clay.

4. A method according to claim 3, wherein said complexing agent is urea. V V

5. A method according to claim 3, wherein the oxidising bleaching agent is selected from the group consisting of hydrogen peroxide, chlorine water ammonium perdisulphate and peracetic acid;

References Cited UNITED STATES PATENTS T J AMES E. POER, Primary Examiner 7 US. Cl. xa. l06288B; 23 -1101 

